Historically, the positioning of onshore pads has involved a number of issues related to proper pad positioning. In the oil and gas industry, for example, proper positioning of onshore pads for oil and gas rigs requires consideration of surface topography and slope constraints. In addition, the orientation of slot templates, which are located on each pad and are used to organize the location of each well on the pad, must also be considered. Finally, each well path—sometimes referred to as a plan from the pad to a selected well target—must be considered.
For example, large scale onshore field development planning creates unique problems for oil and gas companies. Unconventional and tight gas pays generally contain large numbers of subsurface targets to exploit. A direct result is a large number of wells that must be planned and drilled from surface pads or sites, which are analogous to offshore platforms. In order to adequately plan for this, several objectives must be accomplished. The number and location of surface pads or sites required to complete the development is required, for example, which depends on the number of wells that will be drilled from each pad, the engineering constraints placed on the individual well paths (i.e. maximum reach, dogleg severity, inclination angle, etc.), the location of the subsurface targets and the topographic constraints—such as elevation and grade. Slot template geometry and the orientation for each pad also need to be defined. Slot templates generally involve very tight spacing between slots, which requires an understanding of the well paths that will originate from each slot so that collision risk between wells is minimized. And, well paths need to be assigned to the correct slot. Individual well paths may also need to be altered in order to minimize interference with other wells planned or drilled from the same, or different, slot template(s).
The main issue with each objective is the planning cycle time. Planning for 50 pads with 20 wells per pad (i.e. 1000 total wells) can be a tedious, iterative-process subject to trial and error. For instance, a pad is visually positioned over a grouping of targets by visualizing a topographic map. Elevation is eyeballed, estimated and used as the starting reference point elevation. Well locations for the proposed slot template geometry must then be calculated and each individual well path must be assigned to a slot and designed. During the well path design process, it may be determined that the site positioning just did not work due to well path constraints and the process is repeated over and over again until it is successful. At this time, each individual well path must be altered to minimize collision risks with other wells that will be drilled from the same or other sites. The aforementioned process would realistically take anywhere from 3-5 days for just one pad. Multiply this process by 50 and the length of time required becomes significant.
One method for determining platform placement that is most often used may be thought of as a “move and calculate footage” based method. In this method, a series of wellpath plans are created manually, one at a time, using dogleg, inclination, reach, and anti-collision as the planning criteria for the platform location. The cumulative measured depth traversed by the many wellpaths is summed and used as a measurement of the base case location.
Once the wellpaths are created, the well planner then moves the surface location of the base case platform a fixed distance, usually in one of the four compass directions, and recalculates the cumulative measured depth. If the cumulative measured depth decreases from the base case measurement, the well planner knows that there is a potential location which is “better” than the base case location. The planner then goes through many iterations moving the platform location by different distances and to different compass directions from the base case location looking for the best location based on the total calculated footage of the wellpaths that will be required to drill from the wells to the platform location.
The above-mentioned methodology has a number of drawbacks. For example, it is tedious, time consuming, and requires fixing the number of plans and targets to be reached. Using this methodology, it is not unusual for well planners to spend three to four weeks on just one project.
Other automated methods for platform placement use Monte-Carlo or random number based statistical calculations for platform placement and take into account producers vs. injectors, cost of processing facilities, and existing pipelines. They, however, do not take into account target weighting, which is addressed in U.S. Pat. No. 7,200,540. The '540 patent, which is assigned to Landmark Graphics Corporation and is incorporated herein by reference, further addresses the need for a method that varies the number and locations of platforms and optimizes the targets used if the resultant platform set provides a plan that: a) reaches more targets; b) reaches the same number of targets with less distance; or c) reaches the same number of targets, but includes targets with higher weighting values based on the reservoir parameters. In short, the '540 patent describes systems that implement methods for selecting a set of platform locations, determining additional platform locations, and determining an optimum location for each platform location in the set of platform locations.
The '540 patent, however, does not address the need to utilize surface topography for automatically extracting pad elevations after positioning when working on large scale onshore field development planning, especially in mountainous regions. Additionally, the '540 patent does not address the ability to update existing pad elevations using a surface grid or the ability to restrict the placement of pads based on slope constraints.
There is also a need, which is not met by the prior art and which will reduce the risk of collision, to optimize slot template orientations by aligning them on strike with the surface elevation model or rotating them based on the planned trajectories. Due to the tight spacing of slot templates, there is also a need to optimally assign plans to the proper slots and to stagger kick-offs and nudge individual plans.